Embodiments of the present invention generally relate to a bonded-wafer semiconductor device and a method for manufacturing a bonded-wafer semiconductor device, and more particularly, to a bonded-wafer superjunction semiconductor device having at least one trench and a method for manufacturing a bonded-wafer superjunction semiconductor device having at least one trench.
Silicon on insulator (SOI) semiconductors, dielectric isolation (DI) semiconductors and bonded-wafer semiconductor devices are generally known in the art. For example, basic known processes to bond semiconductor wafers include forming a layer of silicon dioxide on one silicon wafer, sometimes referred to as the “handle wafer,” and placing the other wafer on the silicon dioxide and annealing (i.e., generally heating to and holding at a suitable temperature and then cooling at a suitable rate) the stacked wafers to form a bonded-wafer semiconductor device. The annealing/bonding process may include heating the stacked wafers in an annealing furnace for a number of minutes or hours. For example, the stacked wafers may be placed in an annealing furnace at 800-1200° C. for few a minutes to several hours to cause the materials to sufficiently bond. The annealing process may be performed in an inert ambient atmosphere, e.g., nitrogen gas, or in an oxidizing ambient atmosphere, e.g., pure oxygen, oxygen/nitrogen mixture, steam or the like. During a “wet” anneal, i.e., when steam is the ambient, the steam is generated using a mixture of oxygen and hydrogen typically above 800° C. Other known bonding methods include coating a silicon wafer with an oxide layer before placing another wafer on the oxide layer and then annealing the whole stack in a rapid thermal annealer for a few minutes at 800-1200° C.
Other known methods of bonding wafers to form SOI and DI devices include using a liquid oxidant or multiple layers of oxides and/or nitrides between the wafers prior to annealing. Additionally, other methods of bonding wafers to form SOI and DI devices include wetting the surfaces of the silicon wafers with a solution such as water (H2O) and hydrogen peroxide (H2O2) and then pressing the wetted wafers together and drying them prior to annealing/bonding at 800-1200° C.
Still other known wafer bonding methods include bonding n-type semiconductor wafers to p-type semiconductor wafers to form a p-n junction. Plasma etches are used to remove impure oxides on the surfaces of the wafers to be bonded. The plasma etch resultantly leaves a thin polymer layer on the respective surfaces. For example, a carbon-fluorine-hydrogen (CHF3) plasma may be used to etch the surfaces to be bonded. The surfaces are then de-oxidized and coated with a fluorocarbon polymeric layer which generally prevents further oxidation of the surface in air. The polymer coated surfaces are then pressed together and annealed at about 800-1300° C. for 4-6 hours. The elevated temperature drives off the fluorine and the hydrogen leaving the carbon, and thereby forming a bond.
There are generally two types of wafer joining methods prior to annealing, namely, hydrophilic joining and hydrophobic joining. In hydrophilic joining, the surfaces to be joined are cleaned using a method that results in the surfaces being hydrophilic such that the exposed silicon atoms on the bare silicon surface are terminated with hydroxyl (—OH) groups. Once joined, the hydroxyl groups on both surfaces attract each other by hydrogen bonding. In hydrophobic bonding, the cleaning step before joining employs hydrofluoric acid. After the cleaning, the exposed silicon atoms with dangling bonds are terminated with fluorine atoms. The fluorine atoms contribute, in part, to the pre-anneal joining force. During the annealing, the fluorine is generally driven from the joined surface.
It is desirable to provide a bonded-wafer semiconductor device and a method for manufacturing a bonded-wafer semiconductor device. It is also desirable to provide a multi-layer silicon-silicon bonded-wafer semiconductor device and a method for manufacturing a multi-layer silicon-silicon bonded-wafer semiconductor device. Further, it is desirable to provide a multi-layer bonded-wafer semiconductor device having at least one trench and a method for manufacturing a multi-layer bonded-wafer semiconductor device having at least one trench. Even further, it is desirable to provide a multi-layer bonded-wafer superjunction lateral Schottky device and a method of manufacturing a multi-layer bonded-wafer superjunction lateral Schottky device.